GB2086506A

GB2086506A - Anti-skid brake control system

Info

Publication number: GB2086506A
Application number: GB8130104A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1980-10-28
Filing date: 1981-10-06
Publication date: 1982-05-12
Also published as: SE449327B; FR2492752B1; DE3040548C2; FR2492752A1; ES8300053A1; DE3040548A1; IT8124711A0; BR8106894A; JPH0130664B2; US4492413A; GB2086506B; IT1139557B; SE8106323L; ES506588A0; JPS57104447A; ZA816953B

Description

1

SPECIFICATION

Anti-skid brake control This invention relates to an anti-skid brake control apparatus fora vehicular hydraulic brake system of the kind comprising a master cylinder actuable by the brake pedal for a static actuation of the wheel brake cylinders, a control-valve device located in the brake line between the working chamber of the 75 master cylinder and the associated wheel brake cylinders for the purpose of braking pressure control and having a return line from the wheel brake cylinders to an'unpressurised hydraulic reservoir with a hydraulically actuable return-locking device inserted inbetween, and an auxiliary energy supply system.

An anti-skid brake control apparatus of the kind initially referred to is known from German printed and published patent application DE-OS 24 43 545.

This apparatus includes an auxiliary energy supply system with a pressure accumulator for making auxiliary energy constantly available. Inserted be fore the master cylinder is a brake-valve device which supplies auxiliary energy to the master cylin der and from there to the associated wheel brake cylinders when braking. With this arrangement, the sleeve-sealed master-cylinder piston overrides the feed bore and is able to assume any desired -30 intermediate position during a control operation, - with the dynamic circuit being permanently super imposed on the static circuit. This does not allow one to test the sleeve for leaks during a normal braking operation and in the case of anti-skid control. If the sleeves are defective and the auxiliary energy fails, there is virtually no more braking effect attainable when braking. It is, furthermore, a disadvantage of the known device that it works only in conjunction with a hydraulic booster and that a large quantity of auxiliary energy is required to be kept available because the normal braking operation is effected partly dynamically. The power loss of the brake system is correspondingly great and the auxiliary energy supply system is also required to be dimen sioned correspondingly large.

It is an object of the present invention to provide an anti-skid brake control apparatus for a vehicular hydraulic brake system of the kind initially referred to, which, besides being of a simple design affords not only functional reliability but also permits the testing of sleeves at the master-cylinder piston for leaks in the case of a normal braking operation and which permits an energy-saving operation resulting in a low power loss.

According to the invention in its broadest aspect, an anti-skid brake control apparatus for a vehicular 1 hydraulic brake system of the kind referred is characterised in that a separating valve which is normally open is inserted in the brake line between the working chamber of the master cylinder and the associated wheel brake cylinders before the control valve device, which valve is arranged to close when the wheel brake cylinders are controlled in the presence of auxiliary energy pressure, in that an auxiliary energy connecting line discharges into the GB 2 086 506 A 1 brake line between the separating valve and the control-valve device, which connecting line contains a check valve opening in the direction of the wheel brake cylinders, and in that a normally closed return-locking device of the return line will open in the case of a control operation with auxiliary energy available.

It is thereby achieved that, in the case of a normal braking operation, the master cylinder will actuate the wheel brake cylinders statically without requiring auxiliary energy, and that sleeves at the mastercylinder piston are constantly tested for leaks.

When a control action is performed, a hydraulic pump can be operated or a continuously circulating fluid flow can be directed into the brake slip control circuit causing development of pressure in the auxiliary energy connecting line to the individual wheel brake cylinders. At the same time, the auxiliary energy actuates the separating valve resulting in separation of the static line of the master cylinder and opens the return- locking device resulting in the return line being opened for the purpose of reducing the pressure in the wheel brake cylinders to be controlled by discharging into the hydraulic reser- voir.

When the control operation has terminated, the hydraulic pump will be disconnected and the separating valve and the return-locking device will assume their initial position in the event of a decline of auxiliary energy pressure so that, again, a normal braking operation with static actuation of the wheel brake cylinders can take place. That is to say, the present invention requires to have auxiliary energy available only if there occurs the (rare) need for anti-skid control. As a result, the auxiliary energy supply system can be of small dimensions. A power loss of the apparatus does not practically arise by virtue of the regulating pump being operated only rarely, and the apparatus can perform in a very energy-saving manner.

Advantageously, the valves controlled by the pump pressure can be combined to form construction units. The particular advantage of the present invention is that already existing brake systems can be equipped subsequently with the apparatus, because the anti-skid brake control apparatus itself is independent of the version of master cylinder used, which latter may, for example, be of single-type, tandem-type or stepped-piston design. Moreover, the master cylinder will be separated completely from the wheel brake cylinders during a control operation which prevents a reaction of dynamic pressure fluid on the position of the brake pedal or on the pedal-feel. The normal function of the master cylinder is maintained upon failure of the auxiliary energy. The valves which are governed hydraulically by the pump pressure do not only protect a fluid reserve in the brake circuit in the case of the auxiliary energy supply failing but also in the event of a defect occurring in a brake circuit (in multiple-circuit brake systems). The anti-skid brake control apparatus is particularly suitable for automotive vehicles of the lower and the middle class. Another advantage is that the system is able to be operated independently of hydraulic boosting.

2 GB 2 086 506 A 2 In an expedient improvement of the present invention, the return-locking device can be opened directly by auxiliary energy pressure in the case of control operation.

Alternatively, the return-locking device can be opened indirectly by auxiliary energy pressure in the case of control operation. In this arrangement, there is provided in particular an electromagnetically actuable return-locking device which is actuated by an electric signal corresponding to the auxiliary energy pressure.

Suitably, the auxiliary energy supply system corn prises a hydraulic pump which is inserted after the hydraulic reservoir. Advantageously, this pump will perform only in the case of a wheel brake cylinder being controlled. Apart from operating the anti-skid brake control apparatus, the hydraulic pump is expediently designed to feed other hydraulic vehicle units. In doing so, the hydraulic pump is able to perform continuously and will be connected to the anti-skid brake control circuit in the case of a control action exclusively.

In another embodiment of the present invention, one tandem master cylinder and one separating valve for each brake circuit are arranged in a dual-circuit brake system.

Expediently, one single return-locking device can be arranged for in the joint return line of both circuits.

However, as an alternative, each brake circuit may contain a return-locking device.

In an advantageous manner, the separating valve and/or the return-locking device inciude(s) a spring loaded piston having its one end designed as a conical valve.

A particularly compact and favourable arrange ment with respect to costs is the result, if the separating valve and the return-locking device are designed as a valve unit.

The valve unit may have in particular a single 105 spring-loaded working piston having both of its ends designed as conical valves.

In another embodiment of the present invention, a further valve is inserted in the auxiliary energy connecting line subsequent to the hydraulic pump, the valve having a passage for the auxiliary energy connecting line as well as a port fora return line branch connected to the unpressurised hydraulic reservoir.

Expediently, this port is able to be maintained in a closed position when the brake is actuated.

In particular, the further valve can be a conical valve which is actuatable by the master-cylinder piston, which is disposed on the side of the master cylinder remote from the pedal and which is inte grated in the master-cylinder unit.

Each of subsequently equipping an already ex isting brake unit with the actual control components is provided in that the further valve is a separate, hydraulically actuatable valve which is connected to the master cylinder via a line branch and which is kept in its closing position by the working pressure of the master cylinder.

The further valve is designed similarly to the valves mentioned above and includes a working 130 piston having its one end shaped as a conical valve.

A compression spring in the housing of said further valve can be provided to urge the working piston into its closing position. This compression spring is dimensioned such theat the further single valve will open the return line branch to the unpressurised hydraulic reservoir after a control action as well as after an application of the brake, for the purpose of removing residual pressure in the auxili- ary energy supply system.

In a dual-circuit brake system with tandem master cylinder there are suitably provided for each brake circuit a respective hydraulic pump and a respective furthervalve.

In still another embodiment of the present invention, the port of the further valve forthe return line branch is opened only when the dynamic pressure of the hydraulic pump exceeds the pedal force or exceeds the static pressure in the master cylinder.

This allows one to reduce pressure peaks of a pump operated during control action.

In an advantageous arrangement, the further valve is a pedal-actuatable throttle valve disposed on the side of the master cylinder close to the pedal.

Said throttle valve can comprise a truncated-coneshaped valve portion which is connected mechanically to the brake pedal, while the piston-rod end, close to the pedal, of the master-cylinder piston is designed as a valve seat containing an inside longitudinal passage which communicates with the return line branch.

There may be received in the piston rod end in particular, a compression spring which tries to urge the valve portion and the piston-rod end away from each other.

The piston-rod end may include a radially enlarged portion which is sealed relative to the cylinder wall.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, wherein:

Figure 1 is an anti-skid brake control apparatus in accordance with the present invention, Figure 2 is another embodiment of an anti-skid brake control apparatus in accordance with the present invention including combined valve units, Figure 3 is an apparatus similarto Figure 2 with two hydraulic pumps, and Figure4another apparatus with a hydraulic pump driven discontinuously and a throttle-valve device close to the pedal.

Figure 1 shows an anti-skid brake control apparatus 1 comprising a largely-known master cylinder 2 which is designed as a tandem master cylinder and is actuatable by a brake pedal 3 as in conventional practice. The pressure which has been developed during a braking action in the working chambers 22 and 23 of the master cylinder 2 enables a static actuation of the two wheel-brake-cylinders'diagon- als 5,6 and 7, 8 in two separate brake lines 20, 21. Each wheel brake cylinder is connected to a return line 28 extending to an unpressurised hydraulic reservoir4.

Disposed in the two brake lines 20, 21 are normally opened, electromagnetically actuatable 2/2-way z 4 3 GB 2 086 506 A 3 valves 9 which are assigned to the individual wheel brake cylinders 5 to 8, while normally closed, electro-magnetically actuatable 2/2-way valves 10 are inserted accordingly in the return line 28 assigned to the wheel brake cylinders 5 to 8. The control valves 9 and 10 are actuated by an electronic control unit (not shown) in the event of inadmissibly high slip values being recognised between the vehicle tyres and the road surface (i.e. a need for 0 control action). In addition, between the master cylinder and the control valves 9, each brake line 20 or 21 contains a separating valve 24 with a working piston 19 axially slidable in a housing and having its one end designed as a conical valve and its other end urged in the opening direction of the separating valve by means of an inwardly lying compression spring 18 which is supported on the housing.

Subsequent to each separating valve 24 and before the associated control valve 9, each brake line 20,21 has an inlet 1 opening into which is an auxiliary energy connecting line 25 communicating with the unpressurised hydraulic reservoir 4 and containing a filter unit 12 as well as a hydraulic pump 11 inserted after the hydraulic reservoir 4.

In the area of the inlet 1, the auxiliary energy 90 connecting line 25 includes in each brake line 20 or 21 a check valve 26 opening in the direction of the associated wheel brake cylinders. Moreover, the line contains connecting branches 29 which extend to -30 the separating valves 24, terminate on the front face thereof and which are thereby connected to an inner chamber of the separating valve remote from the conical valve end of the piston 19.

Subsequent to the hydraulic pump 11, the auxiii ary energy connecting line 25 extends through a furthervalve 34 which is located at the end of the master cylinder 2 remote from the pedal.

The valve 34 includes a portfor a return line branch 35 communicating with the return line 28. In accordance with the embodiment of Figure 1, the 105 valve 34 is designed as a conical valve switching over upon application of the brake pedal 3 and closing the port of the return line branch 35 thereby, while the auxiliary energy connecting line 25 re mains opened. When the brake pedal 3 is released, the conical valve will clear the return line branch 35.

Arranged in the return line 28 is a return-locking device 27 having a design similarto that of the separating valve 24. Accordingly, a piston 17 with a conical-valve end as well as a compression spring 16 115 are provided, which latter spring urges the piston 17 into the closing position in which the return line 28 is closed. Extending from the auxiliary energy connecting line 25 to the return-locking devive 27 is another line branch 39 via which an inner chamber of the return-locking device 27 is adapted to be acted upon by pressure such that the piston 17 is urged into its opening position in opposition to the force of the compression spring 16.

The mode of operation of the anti-skid brake control apparatus will now be described. When braking, depression of the brake pedal 3, according to Figure 1 to the left, will develop pressure in the working chambers 22 and 23 of the master cylinder 2 and will simultaneously cause the conical valve 34to 130 switch over and close the port of the return line branch 35. The separating valves 24 of the two brake lines 20, 21 as well as the return- locking device 27 assume the position shown so that the wheel brake cylinders 5, 6 or 7, 8 are statically actuatable. The braking pressure introduced is not allowed to escape through the closing check valves 26 into the auxiliary energy connecting line 25.

In the case of a need for control action, i.e. in the event of an imminent locked condition of one or more vehicle wheels, the electronic control unit will start the motordriven hydraulic pump 11, resulting in a development of pressure in the auxiliary energy connecting line 25 which pressure will at the same time switch the separating valves 24 into the closing position and the return-locking device 27 into the opening position. The master cylinder 2 will be separated hydraulically by shutting off the brake lines 20 and 21. Further, depression of the brake pedal 3 is no more possible. Via the check valves 26, the auxiliary energy reaches the individual wheel brake cylinders 5 to 8 dynamically actuating them, with the electromagnetically actuatable control valves 9, 10 being actuated by the electronic control unit corresponding to the respective need for contro 1.

Upon completion of the control action, the hydraulic pump 11 is disconnected resulting in the pressure in the auxiliary energy connecting line 25 declining and the separating valves 24 and the return-locking device 27 being switched by spring force to the initial position shown. This enables the wheel brake cylinders to be actuated again statically by the master cylinder 2. When the brake pedal 3 is released, the conical valve 34 will open and clear the return line branch 35 to the unpressurised hydraulic reservoir 4 so that the residual pressure disposed in the auxiliary energy connecting line 25 may decrease.

Upon failure of a static brake circuit, the other brake circuit will remain intact as is described in the prior art. A constant flow system results therefrom which generates a controlled pressure in the case of a control operation. During control action, the static circuits will be dynamically superimposed or replaced. The valves which are governed hydraulically by the pump pressure safeguard a fluid reserve in the brake circuit in case the auxiliary energy supply should fail or a defect should occur in a brake circuit. The hydraulically controlled valves can be controlled electro-magnetically as well. The anti-skid brake control apparatus in accordance with Figure 1 operates at a maximum pressure level of 150 bar resulting in a low power input and in an altogether low weight and small overall dimensions of the device. The tandem master cylinder is not stressed additionally during control action and does not permit any further pedal depression. The fluctuations of pressure occurring at the solenoid valves are of only a minimal amount.

The embodiment of an anti-skid control apparatus 1 shown in Figure 2 has many of the same components as that of the embodiment in accordance with Figure 1. Like parts have been assigned like reference numerals.

4 GB 2 086 506 A 4 In contrast to the first embodiment, there is provided in Figure 2 for each brake line 20,21 a valve unit 30 which combines the separating valve 24 and the return-locking device 27 of the first embodiment in one unit. According to this, a working piston 31 having two conical valve ends is provided, which is urged in an axial direction by an inwardly lying spring 32 supported on the valve housing in such a mannerthat the return line 28 is closed and the first brake line 20 or the second brake line 21 is opened, provided that the working piston is not acted upon by auxiliary energy.

In another variation of the first-mentioned embodiment, according to Figure 2 a further valve 34 is provided for the purpose of removing the residual pressure in the auxiliary energy connecting line 25 after a control operation, which valve is designed separately from the master cylinder 2. The further valve 34 is similar in its design to the separating valve 24 or the return-locking device 27 of Figure 1 and includes a working piston 37 having a conical valve end and being biased by means of a compression spring 38 in such a manner that the return line branch 35 leading to the return line 28 is normally closed. The interior of the further valve 34 containing the compression spring 38 is connected via a line branch 36 to the first brake line 20.

When the brake pedal 3 is applied, the wheel brake cylinders 5 to 8 will be actuated statically in two separate brake circuits, with the valve units 30 as well as the further valve 34 being switched to the position illustrated.

In the case of control operation, the hydraulic pump 11 driven by an electric motor is started and pressure will be built up in the auxiliary energy connecting line 25 by reason of the check valves 26 which pressure causes the valve units 30 to assume the other switching position. As the brake pedal 3 in its depressed position during control action, the further valve 34 will be maintained in the switching position shown due to the prevailing pressure of the line branch 36. The auxiliary energy is supplied dynamically via the check valves 26 to the wheel brake cylinders. Upon termination of a control action, the hydraulic pump 11 is disconnected, and the valve units 30 move to their initial positions (as shown) resulting in the brake system being able to be actuated statically again.

When the brake pedal 3 is released completely, there is no pressure in the line branch 36 so that the valve 34 is urged into the closing position solely by the (weak) compression spring 38. A residual pressure which is present under certain circumstances in the auxiliary energy connecting line 25 will thus cause opening of the valve 34 after a control action and reduce itself by discharging via the return line branch 35. In the embodiment illustrated in Figure 3 which is similarto the embodiment of Figure 2, each brake circuit is provided with a further valve 34 and a valve unit 30, respectively. The introduction of auxiliary energy is effected by means of two hyd raulic pumps 11 which are adapted to be driven during control operation by a common electric motor 14.

The anti-skid brake control apparatus shown in 130 Figure 4 comprises a tandem master cylinder similar to Figure 1, wherein solenoid separating valves 24 are contained in the two brake lines 20 and 21 to the wheel brake cylinders 5, 6,7, 8. The further valve 34 is designed as a throttle valve and is placed at the end of the master cylinder close to the pedal, with the piston-rod end 51 of the master- cylincer piston close to the bedal serving as a valve seat for a truncated-cone-shaped valve portion 50 which is mechanically coupled to the brake pedal 3. The piston-rod end 51 includes an inside longitudinal passage 52 having an enlarged portion close to the pedal wherein a compression spring 53 is received. This compression spring is so located as to urge the valve portion 50 and the piston-rod end 51 away from each other. The inside longitudinal passage 52 communicates with the return line branch 35 to the unpressurised hydraulic reservoir 4. On the side close to the pedal, the piston-rod end 51 has a radially enlarged portion 54 sealing the mastercylinder piston-rod close to the pedal relative to the cylinder wall. The purpose of this arrangement is that the passage of the auxiliary energy connecting line 25 at the end close to the pedal extends through the unit consisting of the throttle valve and the master cylinder.

The mode of operation of the anti-skid brake control apparatus according to Figure 4 will now be described when the brake pedal 3 is not applied, the throttle valve is closed on account of the force of the restoring springs of the two master-cylinder pistons in opposition to the force of the compression spring 53 so that the return line branch 35 is isolated from the auxiliary energy connecting line 25. Upon de- pression of the brake pedal 3, in the case of a normal braking operation, the closed throttle valve will be moved together with the two master- cylinder pistons to the left, when viewing the drawing, and the wheel brake cylinders 5, 6,7, 8 will be actuated statically with the separating valves 24 being opened. The hydraulic pump 11 is not then in operation. When a control action becomes necessary, the electro-magnetic separating valves 24 which are normally opened will be switched into the closed position eliminating the possibility of static actuation of the wheel brake cylinders thereby. At the same time, the hydraulic pump 11 driven by an electric motor will be started in order to develop auxiliary energy in the auxiliary energy connecting line 25 with the throttle valve closed and in orderto feed this energy in a dynamic way via the check valves 26 to the wheel brake cylinders, with the normally closed return-locking device 27 being opened simultaneously by means of the auxiliary energy pressure in the line branch 39. With the electromagnetic control valves 9 and 10 being respectively connected, pressure can thus be discharged from a wheel brake cylinder to be controlled to the unpressurised hydraulic reservoir 4. The return-locking device 27 may also be governed electro-magnetically.

The throttle valve does not allow development of an inadmissibly large amount of pressure in the dynamic circuit of the auxiliary energy connecting line 25. If, during control action, the dynamic pump i c i:

GB 2 086 506 A 5 pressure exceeds the brake pedal pressure or the static pressure in the master cylinder 2, the throttle valve opens so that pressure peaks of the dynamic circuit will be discharged via the inside longitudinal passage 52 and the return line branch 35 to the hydraulic reservoir 4.

When the auxiliary energy fails and the returnlocking device 27 is closed, the brake system is able to perform conventionally with the wheel brake cylinders being actuated statically.

F Thus, an anti-skid brake control apparatus for a vehicular hydraulic brake system is proposed having a master cylinder actuatable by the brake pedal which renders possible a static actuation of the wheel brake cylinders in the case of a normal braking operation. When the wheel brake cylinders are actuated statically, a return-locking device causes closing of the return line to an unpressurised hydraulic reservoir. Inserted in the brake lines to the wheel brakes cylinders are separating valves which are normally opened and which will close in the case of control action in the presence of auxiliary energy pressure, with a connecting line to the wheel brake cylinders being provided which allows auxiliary energy to be dynamically supplied to the wheel brake cylinders. The return-locking device which is normally closed can provide open passage directly or indirectly in the case of a control operation by virtue of auxiliary energy pressure so that pressure -30 of a wheel brake cylinder to be controlled is able to discharge into the unpressurised hydraulic reservoir. The auxiliary energy pressure can be generated by a hydraulic pump performing during the control action. Likewise, the auxiliary energy supply system can be operated continuously while auxiliary energy 100 is supplied to the anti-skid brake control apparatus only in the case of a wheel brake cylinder being controlled. Separate valve and return-locking device can be structurally combined to form a valve unit. A further valve enables the removal of residual pressures or pressure peaks in the auxiliary energy supply system after or during a case of control action. The anti-skid brake control apparatus is of compact design and affords functional reliability as well as an energy-saving operation. In particular, it can be 110 integrated in existing brake systems by simple adapting arrangements.

Claims

1. An anti-skid brake control apparatus fora vehicular hydraulic brake system of the kind cornprising a master cylinder actuatable by the brake pedal for a static actuation of the wheel brake cylinders, a control-valve device located in the brake line between the working chamber of the master cylinder and the associated wheel brake cylinders for the purpose of braking pressure control and having a return line from the wheel brake cylinders to an unpressurised hydraulic reservoirwith a hydraulically actuatable return- locking device inserted inbetween, and an auxiliary energy supply system, characterised in that a separating valve (24) which is normally open is inserted in the brake line (20 or 21) between the working chamber (22 or 23) of the master cylinder (2) and the associated wheel brake cylinders (5,6 or7,8) before the control valve-device (9, 10), which valve is arranged to close when the wheel brake cylinders are controlled in the presence of auxiliary energy pressure, in that an auxiliary energy connecting line (25) discharges into the brake line (20 or 21) between the separating valve (24) and the control-valve device (9, 10), which connecting line contains a check valve (26) opening in the direction of the wheel brake cylinders, and in that a normally closed return-locking device (27) of the return line (28) will open in the case of a control operation with auxiliary energy pressure available.

2. An apparatus as claimed in claim 1, characte- rised in that the return-locking device (27) can be opened directly by auxiliary energy pressure in the case of control operation.

3. An apparatus as claimed in claim 1, characterised in that the returnlocking device (27) can be opened indirectly by auxiliary energy pressure in the case of control operation.

4. An apparatus as claimed in claim 3, characterised in that an electromagnetically actuatable return-locking device (27) is provided, which is actu- ated by an electric signal corresponding to the auxiliary energy pressure.

5. An apparatus as claimed in anyone of the preceding claims, characterised in that the auxiliary energy supply system comprises a hydraulic pump (11) which is inserted after the hydraulic reservoir (4).

6. An aparatus as claimed in claim 5, characterised in that the hydraulic pump (11) will perform only in the case of a wheel brake cylinder being controlled.

7. An apparatus as claimed in claim 5, characterised in that apart from operating an anti-skid brake control apparatus, the hydraulic pump (11) is designed to feed other hydraulic vehicle units.

8. An apparatus as claimed in any one of the preceding claims, characterised in that one tandem master cylinder and one separating valve (24) for each brake circuit are arranged in a dual-circuit brake system.

9. an apparatus as claimed in anyone of the preceding claims, characterised in that one single return-locking devce (27) is arranged for in the joint return line (28) of both brake circuits (Figure 1).

10. An apparatus as claimed in claims 1 to 8, characterised in that each brake circuit contains a return-locking device (27) (Figures 2 and 3).

11. An apparatus as claimed in anyone of the preceding claims, characterised in that the separating valve (24) and/or the return-locking device (27) include(s) aspring-loaded piston (19) or07) having its one end designed as a conical valve (Figure 1).

12. An apparatus as claimed in claim 10, characterised in that separating valve (24) and returnlocking device (27) are designed as a valve unit (30) (Figures 2 and 3).

13. An apparatus as claimed in claim 12, characterised in that the valve unit (30) disposes of a single spring-loaded working piston (31) having both ends designed as conical valves (Figures 2 and 3).

14. An apparatus as claimed in anyone of claims 6 GB 2 086 506 A 6 6 to 13, characterised in that a further valve (34) is inserted in the auxiliary energy connecting line (25) subsequent to the hydraulic pump (11), the valve having a passage for the auxiliary energy connecting line (25) as well as a port for a return line branch (35) connected to the unpressurised hydraulic reservoir (4).

15. An apparatus as claimed in claim 14, characterised in that the port is maintained closed when the brake is actuated.

16. An apparatus as claimed in claim 15, characterised in that the further valve (34) is a conical valve, which is actuatable by the master- cylinder piston (13), which is disposed on the side of the master cylinder (2) remote from the pedal and which is integrated in the master-cylinder unit (Figure 1).

17. An apparatus as claimed in claim 15, characterised in that the further valve (34) is a separate hydraulically actuatable valve which is connected to the master cylinder via a line branch (36) and which is held in its closing position by the working pressure of the master cylinder (Figures 2 and 3).

18. An apparatus as claimed in claim 17, characterised in that the further valve (34) includes a working piston (37) having its one end shaped as a conical valve.

19. An apparatus as claimed in claim 18, characterised in that a compression spring (38) is provided urging the working piston (37) into its closing position.

20. An apparatus as claimed in anyone of claims 17 to 19, characterised in that in a dual-circuit brake system with tandem master cylinder, there are provided for each brake circuit a respective hydraulic pump (11) and a respective further valve (34) (Figure 3).

21. An apparatus as claimed in claim 14, characterised in that the port of the further valve for the return line branch is opened only when the dynamic pressure of the hydraulic pump (11) exceeds the pedal force or exceeds the static pressure in the master cylinder (2).

22. An apparatus as claimed in claim 21, characterised in that the further valve (34) is a pedal- actuatable throttle valve disposed on the side of the master cylinder (2) close to the pedal (Figure 4).

23. An apparatus as claimed in claim 22, characterised in that the throttle valve comprises a truncated-cone-shaped valve portion (50) coupled mechanically to the brake pedal (3), and in thatthe piston-rod end (51), close to the pedal, of the master-cylinder piston is designed as a valve seat having an inside longitudinal passage (52) connected to the return branch line (35).

24. An apparatus as claimed in claim 23, characterised in that a compression spring (53) is received in the piston-rod end (51) which tries to urge the valve portion (50) and the piston-rod end (51) away from each other.

25. An apparatus as claimed in anyone of claims 22 to 24, characterised in that the piston-rod end (51) includes a radially enlarged portion (54) which is sealed relative to the cylinder wall.

26. An anti-skid brake control apparatus fora vehicular hydraulic brake system substantially as described with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1982. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

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